The answer: Yes... and no.
Yes: Well, when I first joined, I didn't even know who the heck morning musume was. Now I'm an offical Hello! Project fan! :D In fact, I probably have more singles from morning musume than Utada Hikaru (Then again, what did you expect from Up-Front? >.>)
Also, ai otsuka wasn't around either. This time tough, I'd heard of her, just not listened :P Same with GACKT, Jay Chou, Arashi and all the Hello! Project sub groups/solo artists (Such as Goto Maki, Fujimoto Miki, Takahashi Ai, Aa!, Gomattou etc)
Also, I haven't been listening to Angela Aki as much as I used to. So in a sense it has changed.
No: Utada Hikaru is still my favourite artist. Always has been since I found out about her, always will be. I still only really listen to JPop (And most of it mainstream as well) and I'm still a sucker for ballads.